Hi & Welcome to HCM. I appreciate your concern for the your son s elevated ASO titer. An antistreptolysin O titer measures antibodies against bacterial infection caused group A Streptococcus (GAS) like sinusitis. These are normal and healthy responses to fight off an infection, so nothing to worry about its level. The ASO test does not predict whether complications will occur following a strep infection, nor does it predict the type or severity of the disease. ASO antibodies are produced about a week to a month after an initial strep infection. The amount of ASO antibody (titer) peaks at about 3 to 5 weeks after the illness and then tapers off but may remain detectable for several months after the strep infection has resolved. Some children have positive antibody titers for many months after a single infection. Hope the explanation given above could answer your query.